The present invention relates to an information recording and reproduction apparatus for recording and reproducing the digital information signal supplied through a transmission line, or more in particular to an information recording and reproduction apparatus comprising a mechanism for protecting the copyright of the digital information transmitted and recorded, and an information recording and reproduction apparatus capable of reproducing the digital information signal supplied and recorded through a transmission line by temporally expanding it to the desired transmission rate at the time of reproduction.
With the progress of the technology for encoding (digitizing) and compressing the video and audio information and the progress of the digital signal processing LSI represented by the microprocessor and the digital signal processor, melding is becoming possible between AV systems, communication systems and computer systems, with the result that a system called the multimedia is closely watched. One field of the multi-media includes, for example, the cable television (CATV). The CATV which is presently supported by the analog transmission is expected to transfer to the digital transmission in the future. In that case, the information supplied (TV signal) is not only stereotype information such as the analog NTSC signal as currently experienced but also such signals for which the data transmission rate and the image and voice quality (information compression ratio) could be freely set to some degree in accordance with the viewer requirements. Further, transmission of various other digital information as well as TV signal is expected to become possible. The technical information relating to CATV is described, for example, in "Minor Feature: Technical Trend of Cable Television", Journal of the Institute of Television Engineers of Japan, Vol. 47, No. 8, 1993, pp. 1069-1073 and 1082-1087.
A scheme for compression based on the digital signal processing of the video (moving image) information developed so far is the MPEG (Moving Picture Image Coding Expert Group) developed using the motion compensation and the DCT (Discrete Cosine Transform). This scheme is opening the way for a remarkable degree of compression. Generally, the compression ratio and the quality of video information are incompatible with each other. These terms are used differently in accordance with the application and object. According to a report, the quality after compression equivalent to the VTR level for the current TV (NTSC) signal, for example, can be achieved by a transmission rate of about 1.5 Mbps including the audio signal. The TV signal with the transmission rate of about 1.5 Mbps will be called a compressed TV signal hereinafter. The technology for compressing the video information is described in "Minor Feature: Digital Recording Technology and Applications 1-2, Trend of Digital Video Technology and Digital Recording Technology", Vol. 47, No. 6, 1993, pp. 801-806, The Institute of Television Engineers of Japan, pp. 801-806, and in "Trend of Digital Video Transmission Technology", Vol. 47, No. 10, 1993, pp. 1269-1276, issued by the same organization. In the case where information with low transmission rate as described above is transmitted using a transmission channel like CATV having a per channel bandwidth of about 6 MHz, for example, the transmission rate of about 20 to 25 Mbps is possible. The compressed TV signal described above permits transmission of information equivalent to about 12 channels including redundant data.
In the VTR for recording and reproducing digital information for the above-mentioned transmission line of CATV, etc., as disclosed in Nikkei Electronics issued Jul. 19, 1993 (No.586), p. 66, the transmission rate of about 25 Mbps for digital recording and reproduction has become technically realizable even for consumer products with a single-head construction, and about 50 Mbps of transmission rate for such products with a multi-head configuration (two channels), thanks to the development of the high recording density technique and the increased relative speeds between the magnetic head and the tape. The use of a digital VTR recording-reproduction transmission rate of about 25 Mbps makes possible recording of the compressed TV signal described above including redundant data in as many as 12 channels. The above-mentioned qualities and data transmission rates is a specific example.
Also, in the case where video information or audio information is handled as a digital signal, the digital information can be transmitted or recorded without any special discrimination from the program and data handled by computers including video or audio or all other digital information. In other words, the transmission and recording of digital information can be processed regardless of the type of information involved. In the future, therefore, all types of digital information including the program and data handled in computers as well as the TV signal will become capable of being supplied using the transmission line of CATV, etc.
With the above-mentioned techniques, however, in the case where a compressed TV signal representing the simultaneous transmission of a plurality of channels is recorded, except for the case where the viewer (VTR user) desires to record all the channels at the same time, effective and efficient use of the transmission line and VTR (recording medium) is impossible. More specifically, when one desired channel of the compressed TV signal is recorded, for instance, the unrequired channel information is also transmitted and recorded, so that the utilization of the transmission and VTR (recording medium) is as low as less than 10% (for the above-mentioned transmission rate). This is also the case when only a required channel is transmitted and recorded, in which case the utilization of the transmission and VTR (recording medium) is similarly less than 10%. The utilization is even lower for the transmission and recording of the program and data handled in computer equipment low in transmission rate.
In order to solve these problems, a method may be to transmit all types of information at the same transmission rate by improving the data transmission rate of each specific information to the highest transmissible level by such means as temporal compression. In this method, the information with a low transmission rate is increased in transmission rate by temporal compression thereby to shorten the transmission time accordingly. In transmitting the above-mentioned compressed TV signal (1.5 Mbps), for example, the signal is temporally compressed by a factor of 12 thereby to convert the transmission rate to 20 to 25 Mbps including redundant data. In this way, a one-hour program is transmitted and recorded for five minutes, i.e., one twelfth of the time otherwise required.
In the information transmission by transmission rate conversion by temporal compression, however, the temporally compressed signal is required to be temporally expanded on the viewer (information receiver) side. When this temporal expansion is performed using a buffer memory (a memory for storing data temporarily) or the like, a vast amount of memory capacity is required. In the case where a 60-minute program with the transmission rate of 1.5 Mbps is temporally compressed by a factor of 1/12 and transmitted for five minutes at the transmission rate of 18 Mbps, for example, a buffer memory of at least a data quantity corresponding to 55 minutes (about 5 Gbits) is required with the transmission rate of 1.5 Mbps. This involves a very large and very expensive system. Further, in accordance with the increase in the duration of a program, the capacity of the buffer memory is required to be increased. Recording the temporally-compressed information with the same transmission rate is easily realized on the viewer side using the above-mentioned digital VTR. Temporal expansion for reproduction, however, requires a vast capacity of buffer memory is required as in the above-mentioned case.
At present, the system for supplying such information as video software or computer software (including game software) is centered on packaged media (cassette tape, disc or ROM). These software information are supplied in the form of sale or rental (loan). In contrast, improvement in the digital information network and the diffusion of the VTR capable of recording and reproducing digital information are expected to make possible supply of a great amount of software information through the digital information network in place of the packaged media.
The information transmission through the digital information network and the information recording/reproduction by digital VTR described above, however, are accompanied by so low a quality degradation in the process of transmission or recording/reproduction that the copyright of the software information supplied directly through such means cannot be protected. The information like video software thus transmitted would constitute a sold object and therefore it would be difficult to supply such information at as low a price as the video information so far supplied in the form of rental. In other words, if distribution of software Information at as low a prices as the present video rental is to be made possible, some means different from the current protection system is required to protect the copyright of the software information.
In view of this, unlike the past system of copyright protection which is centered on dubbing prevention (anti-duplication), the present invention is based on the notion that the copyrighted information is not used at the time of acquisition or recording of the software information but the use of a copyrighted information occurs at the time of reproduction (reproduction) thereof.